Earth's transmission spectrum from lunar eclipse observations
E. Palle, M.R. Zapatero-Osorio, R. Barrena,P. Montañes-Rodriguez, E. Martin, A. Garcia-Muñoz
Pallé et al. 2009, Nat.
Nowadays we can monitor night lights, atmospheric changes, plankton blooms, forest health, etc...
But, how does our planet look like to ET?
We will need a detailed understanding of the “micro-scale” processes to interpret the observed “macro-scale” properties
When observing an exoplanet, all the light will come from a single point.
Observing the Earth as a planet(no spatial resolution)
Earth–as-a-point observations with a very remote sensor
A compilation of high spatial resolution data into a global spectra or photometry, and modeling
Earthshine Observations: The Earthshine is the ghostly glow on the dark side of the Moon
The Earthshine on the moon
ES/MS = albedo (+ geometry and moon properties)
Leonardo da Vinci, Codex Leicester, 1510
Chappuis Ozone bandB-O2
A-O2
Atmospheric Water vapor
Rayleigh Scattering
Spectral Albedo of the Earth: 2003/11/19
Montañés-Rodriguez et al., ApJ, 2006
Vegetation
But isolating the light from the planet is VERY challenging,what if direct detection is not possible?
What about transiting Earths?
Atmospheric characterization of Hot Jupiters has already been achieved trough transit spectroscopy
We can observe it during a lunar eclipse
NOT, Visible, 0.4-1 μmWHT, Near-IR, 0.9-2.5 μmLa Palma, Canaries
Lunar eclipse August 16th 2008
Umbra
Penumbra
Brigth Moon
Umbra
Umbra/Bright
Bright
Hα
0.5 1.0 1.5 2.0 2.5
Earth’s Transmission Spectrum
The pale red dot
μm
O
2
O
3
Ca II
H2O
Earth’s Transmission SpectrumVisible
0.4 0.5 0.6 0.7 0.8 0.9 μm
O
4
Ca II
Ca IIH
α
NO
2
?
Fraunhofer lines structure
CO
2
H2OO
2
•O
2
1.0 1.25 1.5
O
2
O
2
•O
2
O
2
•N
2
Earth’s Transmission SpectrumNear-IR ZJ
μm
Atmospheric Dimers:
• Van de Waals molecules: Weakly bound complexes
• They are present as minor rather than trace species.
• One likely origin of continuum absorption.
• Observed on Earth (gas) and Jupiter (gas; (H2)2), Ganymede, Europa and Callisto (condensed), and in the laboratory (gas/condensed).
• Never on Venus/Mars, where there must be CO2 – X
• NOT contained in the common spectral libraries
CH
4
CO
2
H2O
1.5 2.0 2.5
Earth’s Transmission SpectrumNear-IR HK
μm
Kaltenegger & Traub 2009
0.5 1.0 1.5 2.0 2.5Palle et al, 2009
How deep we see in the planet atmosphere?
h
T(h, λ)
Traub, 2009
h min ?
• Are antropogenic signatures visible in the lower layers?
• Is there a surface signal?
Evolution of the Earth’s Transmission Spectrum during the eclipse
How deep we see in the planet atmosphere?
Evidences?
Ref.: Kaltenegger & Traub 2009
Reflection vs Transmission
Earth’s Reflectance Spectrum: Earthshine
Same instrumentation only two months apart
0.5 1.0 1.5 2.0 2.5μm
0.5 1.0 1.5 2.0 2.5
Reflected spectrum Transmission Spectrum
CO
2
CH
4
CH
4
O
2
CO
2
Blue planet?
O
2
O
2
•O
2
O
2
•N
2
O
2
•O
2
Palle et al, 2009μm
Thus, the transmission spectrum of telluric planets contains more information for the atmospheric characterization than the reflected spectrum.
And it is also less technically challenging
But, how far are we from making the measurements ?
Terrestrial inner-orbit planets based on their transits:
- About 50 planets if most have R ~ 1.0 Re - About 185 planets if most have R ~ 1.3 Re - About 640 planets if most have R ~ 2.2 Re (Or possibly some combination of the above)
About 12% of the cases with two or more planets per system
CoRoT & KEPLER can provide this input
Many other surveys: Plato, TESS, Ground-based searches, ...
F*
F* - F* ( ) + F*( ) T Aa
____
A*
Ap*a
______
A*
+ Noise
+ Noise
Wavelength (μm)
Differential transit spectroscopy M star + Earth : 1 (2) measurement
Ss+p / Sp
M8 star + 1 Earth ... with the E-ELT
~5 h
~ 150 h~ 50 h
~ 25 h
Wavelength (μm) Wavelength (μm)
Work in progress ...
Still, we must pursue the characterization with direct observations
Exploration of surface featuresPresence of continentsRotational periodLocalized surface biomarkers (vegetation)
Orbital light curve Ocean glints and polarization effects
Conclusions We have obtained the Earths transmission spectra 0.4-
2.5 μm First order detection and characterization of the main
constituents of the Earth's atmosphere Detection of the Ionosphere : Ca II, ( Mg, Fe, ??) Detection of O2•O2 and O2•N2 interactions Offers more information than the reflectance spectra
Using the measured Earth transmission spectrum and several stellar spectra, we compute the probability of characterizing a transiting earth with E-ELT For a Earth in the habitability zone of an M-star, it is
possible to detect H2O , O2 , CH4 ,CO2 (= Life) within a few tens of hours of observations.
Thank you
Thank you
The Ring effect
Rotational Raman Scattering (RRS)
Early evidence:
Sky-scattered Fraunhofer lines were less deep but broader than solar lines
λex
λex-Δλ, λex, λex+Δλfrequency redistributionIncident λ + Stokes +Anti-Stokes branchesincident photon
Incidentexiting
difference/ratio
The Ring effect: Rotational Raman scattering
Transmission spectrumSolar spectrum
Vountas et al. (1998)